1. Field
The present art relates to a screw fastening unit analysis model creation method, recording media, and apparatus of creating an analysis model by subjecting a three-dimensional model of a device having a screw fastening unit to mesh separation and particularly relates to the screw fastening unit analysis model creation method, recording media and apparatus of creating the analysis model in which the meshes of a screw and a screw hole are precisely fit.
2. Description of the Related Art
Recently, in information processing devices such as hard disk drives, along with increased densities of media and improvement of the resistance of the devices to shock, performing examination in advance by analysis of the misalignment caused by temperature variations between members fastened by a screw and analysis of the misalignment between the members caused by shock that takes friction into consideration has become important.
For example, test of cyclically varying the environmental temperature between a normal temperature of 20° C. and a high temperature of 70° C. is sometimes performed as temperature cycling test that takes the usage environment of the devices into consideration; and, when such temperature cycling test is performed, a screw fastening unit in which two members having different thermal expansion conditions with respect to the temperature are fixed has a problem that misalignment between the members is momentarily generated due to the difference in the degree of thermal expansion caused by temperature variation when the screw fastening force is not appropriate, and examination in advance by misalignment analysis is required.
In the misalignment analysis of such members fastened by a screw, a three-dimensional model of a device having the screw-fastened part created by a CAD has to be subjected to mesh separation to create an analysis model which is divided into meshes.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2001-265836    Patent Document 2: Japanese Patent Application Laid-Open Publication No. H09-245072
However, in conventional mesh separation, mesh separation of an outer peripheral circular arc surface which serves as a screw outer shape and mesh separation of an inner peripheral circular arc surface which serves as a screw hole is performed by using triangles or trapezoids, and the edges of the screw and the screw holes are circular arc while the edges of the triangles and trapezoids are straight; therefore, even when the accuracy is enhanced by reducing the mesh size, the mesh-separated circular arc edge of the screw outer periphery and circular arc edge of the hole inner periphery become polygonal mesh edges wherein a plurality of meshes are arranged circularly, and the part in which the meshes of the screw and the screw hole are overlapped or a gap is generated in the engaged part of the screw and the screw hole, and there is a problem that the screw cannot be fixed to the screw hole.
FIGS. 24A and 24B are exploded view of a three-dimensional model of a device which is an analysis object. Screw holes 102 are provided at peripheral upper end portions of a base 100, and it has a structure that a cover 104 is placed on the base 100 and fastened and fixed by screws 106.
FIG. 25 shows part of the base 100 of FIGS. 24A and 24B, wherein the screw 106 is fastened with the screw hole 102 via the cover 104 therebetween. When the base 100 in which the screw hole 102 is provided is subjected to mesh separation (mesh generation) by using triangle meshes, FIGS. 26A to 26C are obtained.
FIG. 26A shows the base 100 which has undergone mesh separation, FIG. 26B is an enlarged view of the part of a screw hole 102-1 thereof, and FIG. 26C is a plan view thereof. The edge of the screw hole 102 before it is subjected to mesh separation is circular arc as shown in FIG. 25; and, when mesh separation is performed by using triangular meshes as shown in FIGS. 26A to 26C, the screw hole 102-1 having a polygonal edge is obtained since triangular meshes are generated along the circular arc edge.
In FIGS. 27A to 27C, the meshes are eliminated without changing the edge of the base 100 after it has undergone the mesh separation of FIGS. 26A to 26C, wherein the screw hole 102-1 is provided as a polygonal cylindrical hole through the mesh separation, and there are projections of the edge in the middle thereof.
FIGS. 28A and 28B show a screw 106-1 which has undergone mesh separation by using triangular meshes; and, since the triangular meshes are generated along a cylindrical surface, it has an uneven prismatic shape having polygonal edges, and the edges are projected or recessed with respect to plane surfaces.
FIGS. 29A and 29B show the screw 106-1 after it has undergone the mesh separation of FIGS. 28A and 28B with the edges thereof unchanged and the meshes eliminated, and it has a prismatic shape having irregularities on the edge surfaces due to the mesh separation. FIG. 29C shows a transparent state.
In order to solve the problem that an overlapped part or a gap is generated in the engaged part of the screw and the screw hole due to the mesh separation of the screw fastening unit and accurate engagement cannot be performed, with respect to a screw fastening unit in which the cover 104 is fastened to the screw hole 102 of the base 100 by the screw 106 of FIG. 30A, the screw 106 is omitted as shown in FIG. 30B, the lower surface of the base 100 having the screw hole 102 is fixed, a contact unit 108 of the upper surface of the cover 104 and the screw 106 is pressed down by screw axial force 110, and the misalignment between the members with respect to temperature variation is analyzed in this state.
However, screw fastening units of the device required to be subjected to misalignment analysis is plural, and, moreover, there is a level difference in some cases due to different heights H1 and H2 of disposed positions 112-1 and 112-2 of the screw holes 102-1 and 102-2 of the base 100 as shown in FIG. 31. When there is a level difference between screw fastening units, the displacement in the base 100 side with respect to thermal expansion and thermal contraction is different depending on the level difference, the thermal expansion and thermal contraction caused by the level difference is not taken into consideration by the fixing method of merely pressing down the contact units 108-1 and 108-2 of the upper surface of the cover 104 with the screws by screw axial force 110-1 and 110-2, and strict misalignment analysis is not performed.